Evaluation of residual charge after a forced extinguishing of the vacuum arc

The paper presents results of an experimental and theoretical analysis concerning the observation of the post-arc phenomena in plasma after the forced extinguishing of a diffuse arc in vacuum. Examination applied, among other things, evaluation of the residual charge. Experiments were performed in laboratory conditions using a de-mountable vacuum chamber equipped with Cu flat contact system. The switched-off arc current had the form of a half-wave with amplitudes of 400 A and 600 A and frequency of 30 Hz. The source of this current was a capacitor bank, loaded before each switching process. The voltage of loaded capacitor was in range of few hundreds Volts, so the examined arc was low voltage and diffuse one. The forced extinguishing had been realised by the counter-pulse current with falling rate in range 2÷90 A/μs. The measurements of post-arc plasma was performed using retarding field analyser (RFA), witch worked in electron separation mode, measuring ion current. The ion current after extinguishing of the arc was the basis to evaluation of the residual charge. The peak post-arc current was the range (2-7) A and residual charge (10-30) μC in the tested conditions. The results could be used in modelling of post-arc phenomena in vacuum.